1. Field of the Invention
The present invention relates generally to characterizing semiconductor materials. More particularly, the present invention involves optical metrology techniques used to determining physical dimensions of a patterned semiconductor material.
2. Description of Related Art
Current integrated circuit (IC) manufacturing processes employ bulk silicon substrates for the fabrication of semiconductor devices. During the manufacturing process, in-line metrology techniques such as spectroscopic ellipsometry (SE) and reflectometry may be used to determine the properties of the substrate. Using these techniques and certain characteristics of the silicon substrate, for example, the optical properties of the substrate, and parameters such as thickness and refractive index of the layers deposited on the silicon substrate may be determined. In most cases, the optical constants are parameterized in some form of an oscillator model or other useful optical model.
Spectroscopic ellipsometry and reflectivity may be used to measure critical dimensions (CD) for lithographic processing of three-dimensional (3D) test structures and lines. These techniques are know as scatterometry and provide a means for determining line height, width, sidewall angle, pitch, and the like from a plurality of parallel lines. Currently, library based scatterometry solutions are developed to analyze scatterometry data and determine line width and shape. Typical library based scatterometry solutions are developed by solving Maxwell's equations and generating different spectral (either reflectivity curves or ellipsometry curves) responses. The measured data of a test structure is then matched to a particular library and the physical dimensions of the test structure are interpolated between the two closest simulated curves. However, Maxwell's equations are the classical solution to electromagnetic wave propagation through a dispersive medium and the dielectric function (optical properties, n, and k) is assumed to remain constant for any physical dimensions. As such, the change in the dielectric function due to quantum confinement is not accounted for.
Any shortcoming mentioned above is not intended to be exhaustive, but rather is among many that tends to impair the effectiveness of previously known techniques for characterizing substrates; however, shortcomings mentioned here are sufficient to demonstrate that the methodologies appearing in the art have not been satisfactory and that a significant need exists for the techniques described and claimed in this disclosure.